Vitamin D Supplements: Reaping the Benefits from the Right Amount

Yvette C. Terrie, BSPharm, RPh

Published Online: Wednesday, June 11, 2014

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Some Patient Populations May Be at Risk for Vitamin D Deficiency
Vitamin D is classified as a fat-soluble vitamin and is synthesized in the skin from endogenous or dietary cholesterol when an individual is exposed to ultraviolet radiation or sunlight.1-5 The primary biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus.1-5 Vitamin D is also present naturally in some foods and is added to others.1-5

Vitamin D has the properties of both a vitamin and a hormone, aids in the absorption of calcium in the gut, and assists in maintaining sufficient serum calcium and phosphate levels to provide normal mineralization of bones.1-5 According to the National Institutes of Health’s Office of Dietary Supplements website, serum concentrations of vitamin D are closely regulated by the parathyroid gland and serum concentrations of calcium and phosphate.1-5 Vitamin D aids in the formation and maintenance of strong bones.1-5 So it is no surprise that an adequate level of vitamin D has a pivotal role in decreasing the risk of fractures from falls.1

Vitamin D is available in 2 forms: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3).1-7 Cholecalciferol is the naturally occurring form of vitamin D, which is synthesized in the skin from endogenous or dietary cholesterol when an individual is exposed to sunlight.1-7 Ergocalciferol is often utilized as a food additive.1-7

Typically, most of the US population obtains a sufficient amount of vitamin D through daily sunlight exposure and dietary means; however, some patient populations may be at a greater risk for vitamin D deficiency, especially due to less sun exposure during the winter (Table 1).1-3 Examples of patients who may be at greater risk for vitamin D deficiency include the elderly, obese individuals, exclusively breast-fed infants, and those who have limited sun exposure.1-3 In addition, patients with fat malabsorption syndromes (eg, cystic fibrosis) or inflammatory bowel disease (eg, Crohn’s disease) are at risk for vitamin D deficiency.1-3

The use of certain medications, such as phenytoin and carbamazepine, may increase the metabolism of vitamin D by increasing the hepatic metabolism of vitamin D to inactive compounds and reducing calcium absorption.1-3 The use of corticosteroids may impair the metabolism of vitamin D; therefore, patients taking these medications should be routinely monitored for adequate vitamin D levels.4-6

Although more research is needed, recent clinical studies have linked low levels of vitamin D to many medical conditions, such as autoimmune disorders, cardiovascular disease, certain cancers, musculoskeletal decline, dementia, infectious disease, and depression.1-4,7 Some clinical studies have reported that a daily intake of 1000 IU of vitamin D may provide various health benefits (Table 2; Table 3).1 In October 2013, the National Institutes of Health announced its plan to conduct a large-scale clinical trial to determine whether vitamin D supplementation may prevent or delay type 2 diabetes mellitus in prediabetic or at-risk individuals.8

OTC Vitamin D SupplementsSeveral vitamin D supplements are available as single-entity products. Some products contain a combination of vitamin D and calcium, and vitamin D is typically found in multivitamin supplement products (Table 4). These supplements are marketed in various dosage forms, including capsules, tablets, liquids, gummies, and sublingual tablets, to meet the specific needs of various patient populations.

Patients may be getting adequate vitamin D through their diet, sun exposure, and multivitamin supplements. Therefore, before using vitamin D supplements, patients should be encouraged to discuss their use with their primary health care provider. When vitamin D supplementation is recommended, vitamin D3—the natural form of vitamin D—is preferred over vitamin D2 because vitamin D3 is most effective in maintaining a sufficient level of vitamin D in the body.1-7

Closing Thoughts
Pharmacists are in a pivotal position to identify patients at risk for vitamin D deficiency and possible drug–nutrient interactions and should make clinical recommendations accordingly. Patients suspected of having a nutritional deficiency should always be referred to their primary health care provider for further medical evaluation, when warranted, prior to a recommendation to use vitamin D supplements. During counseling, patients should be reminded to adhere to recommended dosages unless otherwise directed by their primary health care provider.

The recommended daily upper limit for vitamin D to avoid possible toxicosis is 4000 IU; patients should be alerted to check the vitamin D content in any supplements that they may be taking.1 Although vitamin D toxicosis is rare, patients experiencing any of the signs associated with vitamin D toxicosis (eg, weakness, anorexia, headache, somnolence, nausea, vomiting, dry mouth, a metallic taste, constipation, muscle or bone pain) should immediately consult their primary health care provider.1,4,5 Other possible adverse effects of vitamin D toxicosis include kidney stones, hypercalcemia, and renal failure.1,4,5

Patients—especially those with existing medical conditions and those taking medications that could interact with vitamin D—should be encouraged to discuss the use of vitamin D supplements with their primary health care provider prior to use.

Ms. Terrie is a clinical pharmacist and medical writer based in Haymarket, Virginia.References: